Continuous theta burst stimulation over the left dorsolateral prefrontal cortex decreases medium load working memory performance in healthy humans

Combined noninvasive brain stimulation virtual reality for upper limb rehabilitation poststroke: A systematic review of randomized controlled trials

Upper limb impairments are common consequences of stroke. Noninvasive brain stimulation (NIBS) and virtual reality (VR) play crucial roles in improving upper limb function poststroke. This review aims to evaluate the effects of combined NIBS and VR interventions on upper limb function post-stroke and to provide recommendations for future studies in the rehabilitation field. PubMed, MEDLINE, PEDro, SCOPUS, REHABDATA, EMBASE, and Web of Science were searched from inception to November 2023. Randomized controlled trials (RCTs) encompassed patients with a confirmed stroke diagnosis, administrated combined NIBS and VR compared with passive (i.e., rest) or active (conventional therapy), and included at least one outcome assessing upper limb function (i.e., strength, spasticity, function) were selected. The quality of the included studies was assessed using the Cochrane Collaboration tool. Seven studies met the eligibility criteria. In total, 303 stroke survivors (Mean age: 61.74 years) were included in this review. According to the Cochrane Collaboration tool, five studies were classified as "high quality," while two were categorized as "moderate quality". There are mixed findings for the effects of combined NIBS and VR on upper limb function in stroke survivors. The evidence for the effects of combined transcranial direct current stimulation and VR on upper limb function post-stroke is promising. However, the evidence regarding the effects of combined repetitive transcranial magnetic stimulation and VR on upper limb function is limited. Further randomized controlled trials with long-term follow-up are strongly warranted.

Noninvasive brain stimulation for cognitive rehabilitation following traumatic brain injury: A systematic review

Traumatic brain injury (TBI) can cause numerous cognitive deficits. These deficits are associated with disability and reduction in quality of life. Noninvasive brain stimulation (NIBS) provides excitatory or inhibitory stimuli to the cerebral cortex. This review aimed to examine the effectiveness of NIBS (i.e., rTMS and tDCS) on cognitive functions in patients with TBI. PubMed, SCOPUS, PEDro, CINAHL, MEDLINE, REHABDATA, and Web of Science were searched from inception to May 2021. The risk of bias in the randomized controlled trials was assessed using the Cochrane Collaboration's instrument. The Physiotherapy Evidence Database (PEDro) scale was applied to evaluate the risk of bias in the non-randomized controlled trials. Ten studies met our inclusion criteria. Six studies used repetitive Transcranial Magnetic Stimulation (rTMS), and four used transcranial Direct Current Stimulation (tDCS) as cognitive rehabilitation interventions. The results showed heterogenous evidence for the effects of rTMS and tDCS on cognitive function outcomes in individuals with TBI. The evidence for the effects of NIBS on cognition following TBI was limited. TDCS and rTMS are safe and well-tolerated interventions post-TBI. The optimal stimulation sites and stimulation parameters remain unknown. Combining NIBS with traditional rehabilitation interventions may contribute to greater enhancements in cognitive functions post-TBI.

Working memory performance in disordered gambling and gaming: A systematic review

BACKGROUND

Converging evidence supports that gaming and gambling disorders are associated with executive dysfunction. The involvement of different components of executive functions (EF) in these forms of behavioural addiction is unclear.

AIM

In a systematic review, we aim to uncover the association between working memory (WM), a crucial component of EF, and disordered gaming and gambling. Note that, in the context of this review, gaming has been used synonymously with video gaming.

METHODS

Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), we systematically searched for studies published from 2012 onwards.

RESULTS

The search yielded 6081 records after removing duplicates, from which 17 peer-reviewed journal articles were eligible for inclusion. The association between WM and problem or disordered gaming and gambling have been categorized separately to observe possible differences. Essentially, problem gaming or gambling, compared to disorder, presents lesser severity and clinical significance. The results demonstrate reduced auditory-verbal WM in individuals with gambling disorder. Decreased WM capacity was also associated with problem gambling, with a correlation between problem gambling severity and decreased WM capacity. Similarly, gaming disorder was associated with decreased WM. Specifically, gaming disorder patients had lower WM capacity than the healthy controls.

CONCLUSION

Working memory seems to be a significant predictor of gambling and gaming disorders. Therefore, holistic treatment approaches that incorporate cognitive techniques that could enhance working memory may significantly boost gambling and gaming disorders treatment success.

The Effect of Continuous Theta Burst Stimulation over the Right Dorsolateral Prefrontal Cortex on Cognitive Function and Emotional Regulation in Patients with Cerebral Small Vessel Disease

OBJECTIVES

Cognitive impairment in cerebral small vessel disease (CSVD) is a common cause of vascular dementia and is often accompanied by mental disorders. The purpose of this study was to investigate the effect of continuous theta burst stimulation (cTBS) over the right dorsolateral prefrontal cortex (DLPFC) on the cognitive function and Hamilton depression (HAMD) scores in patients with CSVD.

METHODS

A total of 30 CSVD patients who met the inclusion criteria were randomly assigned to either the sham or cTBS group. The patients in both groups received routine cognitive function training. All the patients were under treatment for 14 sessions, with one session per day (each cTBS conditioning session consisted of three-pulse bursts at 50 Hz repeated at 5 Hz, 80% MT, and 600 pulses). Before and after the treatment, the patients in both groups were evaluated using the Montreal Cognitive Assessment (MoCA), Stroop Color-Word Test (SCWT), Trail Marking Test (TMT), Digital Span Test (DST), and HAMD test. The time to complete the SCWT and TMT were recorded. The scores of the MoCA, DST and HAMD test were recorded.

RESULTS

The HAMD scores in the cTBS group decreased significantly compared to the control (p < 0.05). There were no significant differences in the MoCA (including the MoCA subitems) or DST scores or in the SCWT or TMT completion times between the two groups (p > 0.05). For the HAMD scores and the MoCA subitem visuospatial/executive scores, the SCWT-B and SCWT-C completion times in the two groups both improved significantly before and after treatment (p < 0.05). For the MoCA scores, the DST-backward scores and the TMT-B completion times in the cTBS group improved significantly before and after treatment (p < 0.05). There was no significant difference in the SCWT-A, TMT-A completion times and MoCA subitems naming, attention, language, abstraction, delayed recall, and orientation scores either before or after treatment in the two groups or between the two groups (p > 0.05).

CONCLUSIONS

In this study, cTBS over the right DLPFC decreased the HAMD scores significantly in patients with CSVD but had no significant improvement or impairment effects on cognitive function. cTBS over the right DLPFC could be used to treat CSVD patients with depression symptoms.

Continuous Theta Burst Stimulation to the left anterior medial prefrontal cortex influences metacognitive efficiency

The contribution of the prefrontal areas to visual awareness is critical for the Global Neuronal Workspace Theory and higher-order theories of consciousness. The goal of the present study was to test the potential engagement of the anterior medial prefrontal cortex (aMPFC) in visual awareness judgements. We aimed to temporarily influence the neuronal dynamics of the left aMPFC via neuroplasticity-like mechanisms. We used different Theta Burst Stimulation (TBS) protocols in combination with a visual identification task and visual awareness ratings. Either continuous TBS (cTBS), intermittent TBS (iTBS), or sham TBS was applied prior to the experimental paradigm in a within-participant design. Compared with sham TBS, we observed an increase in participants' ability to judge their perception adequately (metacognitive efficiency) following cTBS but not iTBS. The effect was accompanied by lower visual awareness ratings in incorrect responses. No significant differences in the identification task performance were observed. We interpret these results as evidence of the involvement of PFC in the brain network that underlies metacognition. Further, we discuss whether the results of TMS studies on perceptual metacognition can be taken as evidence for PFC involvement in awareness itself.

Enhancing Visuospatial Working Memory Performance Using Intermittent Theta-Burst Stimulation Over the Right Dorsolateral Prefrontal Cortex

Noninvasive brain stimulation provides a promising approach for the treatment of neuropsychiatric conditions. Despite the increasing research on the facilitatory effects of this kind of stimulation on the cognitive processes, the majority of the studies have used the standard stimulation approaches such as the transcranial direct current stimulation and the conventional repetitive transcranial magnetic stimulation (rTMS) which seem to be limited in robustness and the duration of the transient effects. However, a recent specialized type of rTMS, theta-burst stimulation (TBS), patterned to mimic the natural cross-frequency coupling of the human brain, may induce robust and longer-lasting effects on cortical activity. Here, we aimed to investigate the effects of the intermittent TBS (iTBS), a facilitatory form of TBS, over the right DLPFC (rDLPFC), a brain area implicated in higher-order cognitive processes, on visuospatial working memory (VSWM) performance. Therefore, iTBS was applied over either the rDLPFC or the vertex of 24 healthy participants, in two separate sessions. We assessed VSWM performance using 2-back and 4-back visuospatial tasks before iTBS (at the baseline (BL), and after the iTBS. Our results indicate that the iTBS over the rDLPFC significantly enhanced VSWM performance in the 2-back task, as measured by the discriminability index and the reaction time. However, the 4-back task performance was not significantly modulated by iTBS. These findings demonstrate that the rDLPFC plays a critical role in VSWM and that iTBS is a safe and effective approach for investigating the causal role of the specific brain areas.

Theta Burst Magnetic Stimulation Improves Parkinson’s-Related Cognitive Impairment: A Randomised Controlled Study

Background. Evidence remains mixed as to the effectiveness of repetitive transcranial magnetic stimulation (rTMS) in treating mild cognitive impairment (MCI) in patients with Parkinson’s disease (PD). Objective. In this study, we examined the short- and long-term effects of patterned rTMS. Methods. We randomly assigned 35 patients with PD with MCI to two groups. One group received intermittent theta burst stimulation (iTBS; n = 20), and the other received its sham counterpart (n = 15). The stimulations were applied over the left dorsolateral prefrontal cortex for 10 consecutive weekdays. Measurements based on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and Montreal Cognitive Assessment (MoCA) were conducted at three time points: at baseline, immediately after the last intervention and at 3-month follow-up. Each patient received a 99mTc-TRODAT-1 single-photon emission computed tomography (SPECT) brain scan at baseline. Results. The iTBS group exhibited significantly greater improvement than the sham group did in total RBANS and MoCA scores ( p < .001 for both) immediately after intervention and at the 3-month follow-up. Radiotracer uptake in the bilateral basal ganglion in baseline SPECT was positively correlated with response to iTBS conditioning with respect to improvements in MoCA scores ( p = .021). Conclusion. This randomised controlled trial provides evidence that a consecutive iTBS protocol can achieve a persistent and wide-ranging therapeutic effect in patients with PD with MCI.

The Role of Expectation and Beliefs on the Effects of Non-Invasive Brain Stimulation

Non-invasive brain stimulation (NIBS) techniques are used in clinical and cognitive neuroscience to induce a mild magnetic or electric field in the brain to modulate behavior and cortical activation. Despite the great body of literature demonstrating promising results, unexpected or even paradoxical outcomes are sometimes observed. This might be due either to technical and methodological issues (e.g., stimulation parameters, stimulated brain area), or to participants’ expectations and beliefs before and during the stimulation sessions. In this narrative review, we present some studies showing that placebo and nocebo effects, associated with positive and negative expectations, respectively, could be present in NIBS trials, both in experimental and in clinical settings. The lack of systematic evaluation of subjective expectations and beliefs before and after stimulation could represent a caveat that overshadows the potential contribution of placebo and nocebo effects in the outcome of NIBS trials.

Theta Burst Magnetic Stimulation Improves Parkinson's-Related Cognitive Impairment: A Randomised Controlled Study

Background. Evidence remains mixed as to the effectiveness of repetitive transcranial magnetic stimulation (rTMS) in treating mild cognitive impairment (MCI) in patients with Parkinson's disease (PD). Objective. In this study, we examined the short- and long-term effects of patterned rTMS. Methods. We randomly assigned 35 patients with PD with MCI to two groups. One group received intermittent theta burst stimulation (iTBS; n = 20), and the other received its sham counterpart (n = 15). The stimulations were applied over the left dorsolateral prefrontal cortex for 10 consecutive weekdays. Measurements based on the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and Montreal Cognitive Assessment (MoCA) were conducted at three time points: at baseline, immediately after the last intervention and at 3-month follow-up. Each patient received a 99mTc-TRODAT-1 single-photon emission computed tomography (SPECT) brain scan at baseline. Results. The iTBS group exhibited significantly greater improvement than the sham group did in total RBANS and MoCA scores (p < .001 for both) immediately after intervention and at the 3-month follow-up. Radiotracer uptake in the bilateral basal ganglion in baseline SPECT was positively correlated with response to iTBS conditioning with respect to improvements in MoCA scores (p = .021). Conclusion. This randomised controlled trial provides evidence that a consecutive iTBS protocol can achieve a persistent and wide-ranging therapeutic effect in patients with PD with MCI.

Continuous theta-burst stimulation over the right dorsolateral prefrontal cortex impairs visuospatial working memory performance in medium load task

Previous studies have shown that visuospatial working memory (VSWM) plays a key role in the encoding and processing of visuospatial information. More importantly, there is evidence suggesting the role of frontal and parietal cortical areas in VSWM and especially, the influence of the frontal cortex in regulating goal-directed behavior. However, the functional role of the right dorsolateral prefrontal cortex (rDLPFC) in visuospatial working memory is still unclear. Here, we noninvasively modulated the rDLPFC activity using continuous theta-burst stimulation (cTBS), with the vertex as the control site. Our study aimed to investigate the effects of cTBS over rDLPFC on working memory task (2- and 4-back) performance. Working memory performance was assessed at the baseline and after stimulation. We observed that the working memory performance as measured by discriminability index was impaired after cTBS over rDLPFC in 2-back task, whereas 4-back task performance was not significantly affected. More so, there was no effect on performance after cTBS over the vertex, suggesting a functional role of rDLPFC in VSWM. Our findings demonstrate the involvement of the rDLPFC in VSWM as well as the load-dependent effect of working memory performance. Taken together, our work constitutes a useful addition to the literature and underscores the effectiveness and efficiency of noninvasive brain stimulation in modulating neuro-cognitive activity.

An active role of inferior frontal cortex in conscious experience

In the search for the neural correlates of consciousness, it has remained controversial whether prefrontal cortex determines what is consciously experienced or, alternatively, serves only complementary functions, such as introspection or action. Here, we provide converging evidence from computational modeling and two functional magnetic resonance imaging experiments that indicated a key role of inferior frontal cortex in detecting perceptual conflicts caused by ambiguous sensory information. Crucially, the detection of perceptual conflicts by prefrontal cortex turned out to be critical in the process of transforming ambiguous sensory information into unambiguous conscious experiences: in a third experiment, disruption of neural activity in inferior frontal cortex through transcranial magnetic stimulation slowed down the updating of conscious experience that occurs in response to perceptual conflicts. These findings show that inferior frontal cortex actively contributes to the resolution of perceptual ambiguities. Prefrontal cortex is thus causally involved in determining the contents of conscious experience.

The effect of non-invasive brain stimulation on executive functioning in healthy controls: A systematic review and meta-analysis

In recent years, there has been a heightened interest in the effect of non-invasive brain stimulation on executive functioning. However, there is no comprehensive overview of its effects on different executive functioning domains in healthy individuals. Here, we assessed the state of the field by conducting a systematic review and meta-analysis on the effectiveness of non-invasive brain stimulation (i.e. repetitive transcranial magnetic stimulation and transcranial direct current stimulation) over prefrontal regions on tasks assessing working memory, inhibition, flexibility, planning and initiation performance. Our search yielded 63 studies (n = 1537), and the effectiveness of excitatory and inhibitory non-invasive brain stimulation were assessed per executive functioning task. Our analyses showed that excitatory non-invasive brain stimulation had a small but positive effect on Stop Signal Task and Go/No-Go Task performance, and that inhibitory stimulation had a small negative effect on Flanker Task performance. Non-invasive brain stimulation did not affect performance on working memory and flexibility tasks, and effects on planning tasks were inconclusive.

Assessing the Effects of Continuous Theta Burst Stimulation Over the Dorsolateral Prefrontal Cortex on Human Cognition: A Systematic Review

Theta burst stimulation is increasingly growing in popularity as a non-invasive method of moderating corticospinal networks. Theta burst stimulation uses gamma frequency trains applied at the rhythm of theta, thus, mimicking theta–gamma coupling involved in cognitive processes. The dorsolateral prefrontal cortex has been found to play a crucial role in numerous cognitive processes. Here, we include 25 studies for review to determine the cognitive effects of continuous theta burst stimulation over the dorsolateral prefrontal cortex; 20 of these studies are healthy participant and five are patient (pharmacotherapy-resistant depression) studies. Due to the heterogeneous nature of the included studies, only a descriptive approach is used and meta-analytics ruled out. The cognitive effect is measured on various cognitive domains: attention, working memory, planning, language, decision making, executive function, and inhibitory and cognitive control. We conclude that continuous theta burst stimulation over the dorsolateral prefrontal cortex mainly inhibits cognitive performance. However, in some instances, it can lead to improved performance by inhibiting the effect of distractors or other competing irrelevant cognitive processes. To be precise, continuous theta burst stimulation over the right dorsolateral prefrontal cortex impaired attention, inhibitory control, planning, and goal-directed behavior in decision making but also improved decision making by reducing impulsivity. Conversely, continuous theta burst stimulation over the left dorsolateral prefrontal cortex impaired executive function, working, auditory feedback regulation, and cognitive control but accelerated the planning, decision-making process. These findings constitute a useful contribution to the literature on the cognitive effects of continuous theta burst stimulation over the dorsolateral prefrontal cortex.

Reducing Amygdala Activity and Phobic Fear through Cognitive Top-Down Regulation

The amygdala is critically involved in emotional processing, including fear responses, and shows hyperactivity in anxiety disorders. Previous research in healthy participants has indicated that amygdala activity is down-regulated by cognitively demanding tasks that engage the PFC. It is unknown, however, if such an acute down-regulation of amygdala activity might correlate with reduced fear in anxious participants. In an fMRI study of 43 participants (11 men) with fear of snakes, we found reduced amygdala activity when visual stimuli were processed under high cognitive load, irrespective of whether the stimuli were of neutral or phobic content. Furthermore, dynamic causal modeling revealed that this general reduction in amygdala activity was partially mediated by a load-dependent increase in dorsolateral PFC activity. Importantly, high cognitive load also resulted in an acute decrease in perceived phobic fear while viewing the fearful stimuli. In conclusion, our data indicate that a cognitively demanding task results in a top-down regulation of amygdala activity and an acute reduction of fear in phobic participants. These findings may inspire the development of novel psychological intervention approaches aimed at reducing fear in anxiety disorders.

Combining HF rTMS over the Left DLPFC with Concurrent Cognitive Activity for the Offline Modulation of Working Memory in Healthy Volunteers: A Proof-of-Concept Study

It has been proposed that the effectiveness of non-invasive brain stimulation (NIBS) as a cognitive enhancement technique may be enhanced by combining the stimulation with concurrent cognitive activity. However, the benefits of such a combination in comparison to protocols without ongoing cognitive activity have not yet been studied. In the present study, we investigate the effects of fMRI-guided high-frequency repetitive transcranial magnetic stimulation (HF rTMS) over the left dorsolateral prefrontal cortex (DLPFC) on working memory (WM) in healthy volunteers, using an n-back task with spatial and verbal stimuli and a spatial span task. In two combined protocols (TMS + WM + (maintenance) and TMS + WM + (rest)) trains of stimuli were applied in the maintenance and rest periods of the modified Sternberg task, respectively. We compared them to HF rTMS without a cognitive load (TMS + WM −) and control stimulation (TMS − WM + (maintenance)). No serious adverse effects appeared in this study. Among all protocols, significant effects on WM were shown only for the TMS + WM − with oppositely directed influences of this protocol on storage and manipulation in spatial WM. Moreover, there was a significant difference between the effects of TMS + WM − and TMS + WM + (maintenance), suggesting that simultaneous cognitive activity does not necessarily lead to an increase in TMS effects.

The use of repetitive transcranial magnetic stimulation (rTMS) following traumatic brain injury (TBI): A scoping review

There is continued interest in developing effective and innovative treatment approaches to manage and improve outcomes after traumatic brain injury (TBI). Included in this, is the potential use of repetitive transcranial magnetic stimulation (rTMS), a neuromodulatory tool currently recommended by the National Institute for Health and Care Excellence as a treatment for depression. This review considers the application of rTMS after TBI, focussing on its therapeutic efficacy for a broad range of sequalae, whether an optimal and safe rTMS protocol can be determined, and recommendations for future clinical and research work. Five research databases (MEDLINE, CINAHL, PsychINFO, SCOPUS, and Web of Science) were electronically searched, identifying 30 empirical studies (single and multiple subject case reports; randomized controlled trials) for the full review. Evidence suggests that rTMS has the potential to be an efficacious therapeutic intervention for multiple symptoms after TBI, including depression, dizziness, central pain, and visual neglect. However, the picture is less encouraging for prolonged disorders of consciousness and mixed for cognitive outcomes. Overall, rTMS was well-tolerated by patients, although some incidents of side effects and seizures have been reported. Recommendations are made for more comprehensive guidelines and sufficient reporting of rTMS parameters and procedures.

The role of the dorsolateral prefrontal cortex in the motor placebo effect

The neural correlates of the placebo effect in the motor domain are still unknown. The aim of this study was to tackle the role of a frontal cortical region, the dorsolateral prefrontal cortex (dlPFC). To this end, we stimulated the cortical site corresponding to the left dlPFC with transcranial direct current stimulation (tDCS) during a placebo procedure and measured any change in the motor placebo effect in all the participants and more specifically in placebo-responders. Three different experiments were conducted in which healthy volunteers performed a force motor task with the index finger. The placebo treatment consisted of transcutaneous electrical nerve stimulation (TENS). In Experiment 1 (expectation alone), participants were only verbally suggested about the positive effects of TENS. In Experiment 2 (expectation and conditioning), participants were verbally suggested about TENS and conditioned with a surreptitious increase in a visual feedback of force. In Experiment 3 (control procedure), participants were told that TENS was inefficient. Each participant was tested in three different days with anodal, cathodal and sham tDCS over the dlPFC. Results showed that in Experiment 1 and 2 force increased after the procedure, independently of tDCS. By focusing on placebo-responders, we found that in Experiment 1 force remained stable after active tDCS, whereas it increased after inactive tDCS. These findings bring new evidence on the neural underpinnings of the motor placebo effect, by showing that independently of the polarity, active tDCS over the left dlPFC may undermine the expectation-induced enhancement of force in placebo-responders.

Working Memory Load-related Theta Power Decreases in Dorsolateral Prefrontal Cortex Predict Individual Differences in Performance

Holding information in working memory (WM) is an active and effortful process that is accompanied by sustained load-dependent changes in oscillatory brain activity. These proportional power increases are often reported in EEG studies recording theta over frontal midline sites. Intracranial recordings, however, yield mixed results, depending on the brain area being recorded from. We recorded intracranial EEG with depth electrodes in 13 patients with epilepsy who were performing a Sternberg WM task. Here, we investigated patterns of theta power changes as a function of memory load during maintenance in three areas critical for WM: dorsolateral prefrontal cortex (DLPFC), dorsal ACC (dACC), and hippocampus. Theta frequency power in both hippocampus and dACC increased during maintenance. In contrast, theta frequency power in the DLPFC decreased during maintenance, and this decrease was proportional to memory load. Only the power decreases in DLPFC, but not the power increases in hippocampus and dACC, were predictive of behavior in a given trial. The extent of the load-related theta power decreases in the DLPFC in a given participant predicted a participant's RTs, revealing that DLPFC theta explains individual differences in WM ability between participants. Together, these data reveal a pattern of theta power decreases in the DLPFC that is predictive of behavior and that is opposite of that in other brain areas. This result suggests that theta band power changes serve different cognitive functions in different brain areas and specifically that theta power decreases in DLPFC have an important role in maintenance of information.

Continuous theta-burst stimulation over the dorsolateral prefrontal cortex inhibits improvement on a working memory task

Theta-burst stimulation (TBS) over the dorsolateral prefrontal cortex (DLPFC) may be more effective for modulating cortical excitability compared to standard repetitive transcranial magnetic stimulation. However, the impact of intermittent (iTBS) and continuous TBS (cTBS) on working memory (WM) is poorly studied. The aim of our study was to compare the effects of iTBS and cTBS on WM over the left and right DLPFC. iTBS, cTBS or sham stimulation was administered over the right and left hemisphere of fifty-one healthy human subjects. WM was assessed before and after TBS using the 1-back, 2-back, and 3-back tasks. We found classical practice effects in the iTBS and the sham group: WM performance improved following stimulation as measured by the discriminability index. However, this effect could not be observed in the cTBS group. We did not find any hemisphere-dependent effects, suggesting that the practice effect is not lateralized, and TBS affects WM performance in a comparable manner if administered either over the left or the right hemisphere. We propose that our findings represent a useful addition to the literature of TBS-induced effects on WM. Moreover, these results indicate the possibility of clarifying processes underlying WM performance changes by using non-invasive brain stimulation.

The effects of individualised intermittent theta burst stimulation in the prefrontal cortex: A TMS-EEG study

Recent studies have highlighted variability in response to theta burst stimulation (TBS) in humans. TBS paradigm was originally developed in rodents to mimic gamma bursts coupled with theta rhythms, and was shown to elicit long-term potentiation. The protocol was subsequently adapted for humans using standardised frequencies of stimulation. However, each individual has different rhythmic firing pattern. The present study sought to explore whether individualised intermittent TBS (Ind iTBS) could outperform the effects of two other iTBS variants. Twenty healthy volunteers received iTBS over left prefrontal cortex using 30 Hz at 6 Hz, 50 Hz at 5 Hz, or individualised frequency in separate sessions. Ind iTBS was determined using theta-gamma coupling during the 3-back task. Concurrent use of transcranial magnetic stimulation and electroencephalography (TMS-EEG) was used to track changes in cortical plasticity. We also utilised mood ratings using a visual analogue scale and assessed working memory via the 3-back task before and after stimulation. No group-level effect was observed following either 30 or 50 Hz iTBS in TMS-EEG. Ind iTBS significantly increased the amplitude of the TMS-evoked P60, and decreased N100 and P200 amplitudes. A significant positive correlation between neurophysiological change and change in mood rating was also observed. Improved accuracy in the 3-back task was observed following both 50 Hz and Ind iTBS conditions. These findings highlight the critical importance of frequency in the parameter space of iTBS. Tailored stimulation parameters appear more efficacious than standard paradigms in neurophysiological and mood changes. This novel approach presents a promising option and benefits may extend to clinical applications.

Theta-burst stimulation causally affects side perception in the Deutsch's octave illusion

Deutsch’s octave illusion is produced by a sequence of two specular dichotic stimuli presented in alternation to the left and right ear causing an illusory segregation of pitch (frequency) and side (ear of origin). Previous studies have indicated that illusory perception of pitch takes place in temporo-frontal areas, whereas illusory perception of side is primarily associated to neural activity in parietal cortex and in particular in the inferior parietal lobule (IPL). Here we investigated the causal role of left IPL in the perception of side (ear of origin) during the octave illusion by following its inhibition through continuous theta-burst stimulation (cTBS), as compared to the left posterior intraparietal sulcus (pIPS), whose activity is thought to be unrelated to side perception during the illusion. We observed a prolonged modification in the side of the illusory perceived tone during the first 10 minutes following the stimulation. Specifically, while after cTBS over the left IPS subjects reported to perceive the last tone more often at the right compared to the left ear, cTBS over left IPL significantly reverted this distribution, as the number of last perceived tones at the right ear was smaller than at the left ear. Such alteration was not maintained in the successive 10 minutes. These results provide the first evidence of the causal involvement of the left IPL in the perception of side during the octave illusion.

The effects of theta burst stimulation (TBS) targeting the prefrontal cortex on executive functioning: A systematic review and meta-analysis

Theta burst stimulation (TBS) is a highly efficient repetitive transcranial magnetic stimulation (rTMS) variant employed in experimental and clinical treatment paradigms. Despite widespread usage of TBS targeting the prefrontal cortex (PFC), there has been no systematic review of the evidence linking TBS protocols to changes in task performance on common measures of prefrontal function in general, and executive functions specifically. A systematic review of the literature was conducted using PsycINFO, PubMed, Web of Science and Scopus databases to identify articles examining the effects of TBS targeting the PFC on executive function task performance. Both the up-regulating (intermittent theta burst stimulation; iTBS) and down-regulating (continuous theta burst stimulation; cTBS) variants of TBS were considered. 32 (29 cTBS; 8 iTBS) studies met the inclusion criteria. Participants (n = 759; 51.41% female) were primarily young adults (M_age = 26), with one study examining the effects of cTBS and iTBS in older adults. Results from individual studies were converted to Hedge's g and random-effects models were used to estimate the overall effect size for each protocol. Age, biological sex, and control methodology were examined as potential moderators of the cTBS effect on executive function test performance. Findings indicated a- reliable attentuating effect of cTBS on executive function task performance (g = -.244, Z = -5.920, p < .001); this effect was relatively uniform across included studies (Q= 24.178, p = .838, I² = 0). Although no significant moderators of the cTBS effect were identified, laterality sub analyses indicated that the magnitude of the effect was significantly higher (M_diff = .213, Z_diff = 2.546, p = .011) for left-sided (g = -.358, Z = -5.816, p < .001) relative to right-sided (g = -.145, Z = -2.552, p = .011) PFC stimulation. A systematic review of iTBS studies revealed variability in reliability of effects though most were in the theorized direction. TBS protocols appear to be effective in modulating prefrontal cortical excitability in previously theorized directions.

Neural correlates for naming disadvantage of the dominant language in bilingual word production

The present study investigated the neural correlates of naming disadvantage of the dominant language under the mixed language context. Twenty one unbalanced Chinese-English bilinguals completed a cued picture naming task while being scanned with functional magnetic resonance imaging (fMRI). Behavioral results showed that naming pictures in the second lanuage (L2) was significantly slower than naming pictures in the first language (L1) under a single language context. When comparing picture naming in L2 to naming in L1, enhanced activity in the left inferior parietal lobule and left cerebellum was observed. On the contrary, naming pictures in Chinese (L1) was significantly slower than naming in English (L2) under the mixed language context. The fMRI results showed that bilateral inferior frontal gyri, right middle frontal gyrus, and right supplementary motor area were activated to a greater extent in L1 than in L2. These results suggest that the dominant language is inhibited to a greater extent to ensure the production of the second language under the mixed language context. Therefore, more attentional control resources are recruited when bilinguals produced the dominant language. The present study, for the first time, reveals neural correlates of L1 naming disadvantage under the mixed language context.

The relationship between dlPFC activity during unpredictable threat and CO2-induced panic symptoms

Panic disorder is characterized by sudden, repeated, and unexpected attacks of intense fear and overwhelming anxiety about when another attack may strike. Patients with panic disorder and healthy individuals with a history of panic attacks show a hypersensitivity to unpredictable threats, suggesting a possible link between panic and sustained anxiety. The purpose of this study was to determine the degree to which induced symptoms of panic relate to fear and anxiety, as well as activity in the neural systems that mediate and regulate these affective states. Psychological and physiological symptoms of panic were assessed during an 8-min 7.5% CO₂ challenge task. Psychological, physiological, and neural symptoms of fear and anxiety were measured during two sessions (one psychophysiology and one functional magnetic resonance imaging where subjects experienced several blocks of no threat (N), predictable shock (P), and unpredictable shock (U; NPU threat task). We used a principle component analysis to characterize panic susceptibility (PS), and found that PS significantly predicted dorsolateral prefrontal cortex (dlPFC) activity to the unpredictable cue during the NPU threat task. When examining the weighted beta coefficients from this analysis, we observed that self-reported fear/anxiety during the CO₂ challenge negatively loaded onto dlPFC activity during the NPU task. Consistent with this observation, dlPFC activity during the unpredictable cue was also negatively correlated with anxiety during the NPU sessions. Together, these results suggest that panic symptoms and anxiety are regulated by the same prefrontal cognitive control system.

No effects of transcranial DLPFC stimulation on implicit task sequence learning and consolidation

Neurostimulation of the dorsolateral prefrontal cortex (DLPFC) can modulate performance in cognitive tasks. In a recent study, however, transcranial direct current stimulation (tDCS) of the DLPFC did not affect implicit task sequence learning and consolidation in a paradigm that involved bimanual responses. Because bimanual performance increases the coupling between homologous cortical areas of the hemispheres and left and right DLPFC were stimulated separately the null findings may have been due to the bimanual setup. The aim of the present study was to test the effect of neuro-stimulation on sequence learning in a uni-manual setup. For this purpose two experiments were conducted. In Experiment 1, the DLPFC was stimulated with tDCS. In Experiment 2 the DLPFC was stimulated with transcranial magnetic stimulation (TMS). In both experiments, consolidation was measured 24 hours later. The results showed that sequence learning was present in all conditions and sessions, but it was not influenced by stimulation. Likewise, consolidation of sequence learning was robust across sessions, but it was not influenced by stimulation. These results replicate and extend previous findings. They indicate that established tDCS and TMS protocols on the DLPFC do not influence implicit task sequence learning and consolidation.

Impact of Prefrontal Theta Burst Stimulation on Clinical Neuropsychological Tasks

Theta burst stimulation (TBS) protocols hold high promise in neuropsychological rehabilitation. Nevertheless, their ability to either decrease (continuous, cTBS) or increase (intermittent, iTBS) cortical excitability in areas other than the primary motor cortex, and their consistency modulating human behaviors with clinically relevant tasks remain to be fully established. The behavioral effects of TBS over the dorsolateral prefrontal cortex (dlPFC) are particularly interesting given its involvement in working memory (WM) and executive functions (EF), often impaired following frontal brain damage. We aimed to explore the ability of cTBS and iTBS to modulate WM and EF in healthy individuals, assessed with clinical neuropsychological tests (Digits Backward, 3-back task, Stroop Test, and Tower of Hanoi). To this end, 36 participants were assessed using the four tests 1 week prior to stimulation and immediately following a single session of either cTBS, iTBS, or sham TBS, delivered to the left dlPFC. No significant differences were found across stimulation conditions in any of the clinical tasks. Nonetheless, in some of them, active stimulation induced significant pre/post performance modulations, which were not found for the sham condition. More specifically, sham stimulation yielded improvements in the 3-back task and the Color, Color-Word, and Interference Score of the Stroop Test, an effect likely caused by task practice. Both, iTBS and cTBS, produced improvements in Digits Backward and impairments in 3-back task accuracy. Moreover, iTBS increased Interference Score in the Stroop Test in spite of the improved word reading and impaired color naming, whereas cTBS decreased the time required to complete the Tower of Hanoi. Differing from TBS outcomes reported for cortico-spinal measures on the primary motor cortex, our analyses did not reveal any of the expected performance differences across stimulation protocols. However, if one considers independently pre/post differences for each individual outcome measure and task, either one or both of the active protocols appeared to modulate WM and EF. We critically discuss the value, potential explanations, and some plausible interpretations for this set of subtle impacts of left dlPFC TBS in humans.

Theta-burst transcranial magnetic stimulation to the prefrontal or parietal cortex does not impair metacognitive visual awareness

Neuroimaging studies commonly associate dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex with conscious perception. However, such studies only investigate correlation, rather than causation. In addition, many studies conflate objective performance with subjective awareness. In an influential recent paper, Rounis and colleagues addressed these issues by showing that continuous theta burst transcranial magnetic stimulation (cTBS) applied to the DLPFC impaired metacognitive (subjective) awareness for a perceptual task, while objective performance was kept constant. We attempted to replicate this finding, with minor modifications, including an active cTBS control site. Using a between-subjects design for both DLPFC and posterior parietal cortices, we found no evidence of a cTBS-induced metacognitive impairment. In a second experiment, we devised a highly rigorous within-subjects cTBS design for DLPFC, but again failed to find any evidence of metacognitive impairment. One crucial difference between our results and the Rounis study is our strict exclusion of data deemed unsuitable for a signal detection theory analysis. Indeed, when we included this unstable data, a significant, though invalid, metacognitive impairment was found. These results cast doubt on previous findings relating metacognitive awareness to DLPFC, and inform the current debate concerning whether or not prefrontal regions are preferentially implicated in conscious perception.